Ion implantation is a process of depositing chemical species into a substrate by direct bombardment of the substrate with energized ions. In semiconductor manufacturing, ion implanters are used primarily for doping processes that alter the type and level of conductivity of target materials. A precise doping profile in an integrated circuit (IC) substrate and its thin-film structure is important for proper IC performance. To achieve a desired doping profile, one or more ion species may be implanted in different doses and at different energies.
In some ion implantation processes, a desired doping profile is achieved by implanting ions in a target substrate at high temperatures (e.g., between 150-600° Celsius). Heating the target substrate can be achieved by supporting the substrate on a heated platen during the ion implantation process. A typical heated platen includes a heated platen portion for supporting and heating a substrate, and a cold base plate that is coupled to a backside of the platen portion and that is adapted to be connected to a scanning mechanism. The platen portion and the base plate are often provided with interconnected internal fluid conduits configured to convey a gas (commonly referred to as a “backside gas”) from a gas source to gaps formed between the platen portion and a substrate. Providing gas in these gaps can enhance thermal contact between the platen and the substrate, which is important if the substrate is to be heated during processing operations.
Such heated platen configurations are associated with a number of challenges. For example, the platen portion and the base plate must be coupled to one another in a manner that provides sufficient mechanical strength to withstand acceleration forces during movement of the platen by the scanning mechanism. Additionally, the hot platen portion should be thermally insulated from the cold base plate in order to minimize heat flow therebetween that could otherwise produce cold spots in the platen portion. Furthermore, since dielectric materials (e.g., ceramics) are generally brittle and are prone to fracture under stress, the platen portion must be coupled to the base plate in a manner that presents minimal resistance to expansion and contraction of the platen portion when it is heated and cooled. Still further, since the presence of gas or other foreign matter in the high vacuum environment of the platen may be detrimental to ion implantation processes, the platen portion and the base plate must be coupled to one another in a manner that provides substantially leak-free transport of gas therebetween.
In view of the foregoing, it will be understood that there is a need to provide a platen support structure that provides strong mechanical coupling, good thermal insulation, and leak-free gas transport between a heated platen portion and a cold base plate while facilitating thermal expansion and contraction of the platen portion without causing damage thereto.